1. Field of the Invention
This invention relates to an adapter unit, and more particularly to an adapter unit which is comprised of a first adapter and a second adapter.
2. Description of the Related Art
Conventionally, there has been proposed a connector comprised of a first hollow cylinder wall, connector terminals, a seal member, and a seal member holder (see Japanese Laid-Open Patent Publication (Kokai) No. 2007-323905).
The first hollow cylinder wall is formed on a wall of a case which accommodates electrical components in a sealed state. The first hollow cylinder wall has an outer peripheral surface formed with eight engaging protrusions at equally-spaced intervals in a circumferential direction. Further, the outer peripheral surface of the first hollow cylinder wall is formed with first and second positioning ribs. Each of the first and second positioning ribs is at an intermediate location between the two adjacent engaging protrusions. Although a foremost end of the first positioning rib has a fixed width, a rear end of the first positioning rib is not uniform in width, but becomes wider as closer to the rearmost end. The second positioning rib has a fixed width, which is the same as that of the foremost end of the first positioning rib. The first positioning rib and the second positioning rib are separately placed from each other by 90 degrees in the circumferential direction of the first hollow cylinder wall.
The seal member holder includes a second hollow cylinder wall, and a third hollow cylinder wall that has a smaller diameter than that of the second hollow cylinder wall, and is concentrically connected to the second cylindrical wall. The second hollow cylinder wall is formed with engaging holes at equally-spaced intervals in the circumferential direction, which are engaged with the engaging protrusions on the first hollow cylinder wall. The engaging holes are away from an end edge of the second hollow cylinder wall. Four groove-like cutouts are formed in an outer peripheral surface of the second hollow cylinder wall at equally-spaced intervals in the circumferential direction. Two of the four cutouts are first and second positioning cutouts which are capable of being fitted to the first and second positioning ribs. A width of the first positioning cutout corresponds to that of the first positioning rib. A width of the second positioning cutout corresponds to that of the second positioning rib.
To assemble this connector, first, the connector terminals and the seal member are disposed inside the first hollow cylinder wall. A gap between the connector terminals and the wall of the case is sealed with the seal member.
Next, the foremost end of the second hollow cylinder wall of the seal member holder is mounted on the first hollow cylinder wall, and the seal member holder is turned. When the first positioning cutout matches the first positioning rib, and the second positioning cutout matches the second positioning rib, the seal member holder is pushed toward the wall of the case, whereby the entire seal member holder is mounted on the first hollow cylinder wall.
To accurately fit the first hollow cylinder wall and the second hollow cylinder wall, it is required to mount the second hollow cylinder wall on the first hollow cylinder wall, and turn the second hollow cylinder wall until the first and second positioning cutouts and the first and second positioning ribs match each other, as described above. However, when the first and second positioning cutouts pass the first and second positioning ribs, there is a fear that the foremost ends of the first and second positioning ribs are caught in the first and second positioning cutouts, causing breakage of the foremost ends of the first and second positioning ribs.